DE4000557C2 - Control device for a vehicle, in particular a motor vehicle - Google Patents

Description

The present invention relates to a control device according to the Preamble of claim 1, that is in or for a four-wheel steering vehicle, where the rear wheels are steered together with the front wheels.

From DE-OS 31 39 792 a wheel suspension for a rear axle of Motor vehicles known, each with two actuating cylinders for pivoting the Wheel guide member or the wheel dependent and / or regardless of the driving condition of the vehicle, so that as possible by the wheel suspension in every driving condition favorable driving characteristics are given.

From DE-OS 38 19 837 is a generic steering-dependent control device for Characteristics in the driving behavior of a vehicle, the suspension, the Shock absorber, the control of the rear wheels of a four-wheel steering system or the like. is controlled. The steering angle is used as a control parameter for the vehicle suspension used. The control system further includes a steering angle sensor Monitoring the steering wheel deflection.

It is also known that a four-wheel steering vehicle is basically a steering system of the rear wheels with a steering angle depending on the steering angle of the front wheels on the basis of a predetermined rear wheel steering characteristic, which is selected with respect to the front wheels, the Suspension characteristics can be corrected in a conventional manner.

As described above, it is in a four-wheel steering vehicle in which the Suspension characteristic is changeable, usual that the suspension characteristic is changeable, that the suspension characteristic is changed independently of the control via the steering of the rear wheels.

The invention is accordingly based on the object of a control device provide with which the control of the suspension characteristic with the Steering control is connected in such a way that the ability to steer or steer (Driving behavior) of the vehicle is improved.  

According to the invention, the object outlined above is achieved by a Control device for a vehicle as set out in claim 1.

The subclaims represent further developments of the inventive concept to solve the mentioned task.

With the aid of the arrangement described above, the control device according to achieve a suitable driving behavior of the present invention, namely the Rear wheel steering characteristic synchronized with the change in the suspension characteristic is corrected.

If the rear wheel steering characteristic is on the opposite phase side with respect to corrected the front wheels in sync with the change in suspension characteristics with a decreasing tendency to understeer, this can decreasing tendency to understeer are promoted, creating a sporty Driving behavior of the vehicle and a leadership or driving stability are improved.

In contrast, if the rear wheel steering characteristic to the opposite phase side related to the front wheels in synchronism with the suspension characteristics an increasing understeer tendency is corrected, the increasing The tilt of the understeer is blocked and canceled, causing an impact the steering characteristic is reduced to the leadership or the drive, with which Driving behavior is improved.

With reference to drawings, the invention is preferred below Exemplary embodiments explained in more detail.

Fig. 1 shows a side view of a vehicle in which an embodiment is applied according to the present invention;

Figs. 2A and 2B each show a schematic representation of an embodiment of an oil pressure circuit, to be used for the present invention;

Figs. 3A to 3C each show an example of control systems for performing control over flow rates.

Fig. 3D illustrates an example of control systems for the displacement of a suspension characteristic between softer and harder conditions.

Fig. 4 illustrates in a diagram an example of switches to be used for shifting the suspension characteristics.

Fig. 5 illustrates an example in a diagram, according to the rear wheel steering characteristics are set.

Fig. 6 shows a top view of an example of a rear-wheel steering unit.

Now the preferred embodiments are detailed described. To this end, the present invention is under He details with reference to the accompanying drawings purifies. In the drawings there are individual reference symbols or symbols subordinate letters "F" and "R" ver has been used to designate front or rear elements, and the subordinate letters "F" and "R" Letters "L" and "R" mean left and right elements, respectively or facilities. For example, the reference means symbol "FL" a left front, and the reference symbol "FR" means a right front, while the reference symbol "RL" and "RR" a left rear side or a right back mean.

Fig. 1 illustrates a sketch of a suspension device of a vehicle such as a motor vehicle.

As shown in FIG. 1, a vehicle body has two front wheels 2 F and two rear wheels 2 R. A fluid cylinder 3 is arranged between the vehicle body 1 and each of the front wheels 2 F. In a corresponding manner, a fluid or liquid cylinder 3 is provided between the vehicle body 1 and each of the rear wheels 2 R. The fluid cylinder 3 comprises a cylinder body 3 a and a piston 3 b, which is housed in the cylinder body 3 a and which defines a liquid pressure chamber 3 c. The piston 3 b is connected to a rod 3 d, which in turn is connected to the vehicle body 1 at its upper end part. The cylinder body 3 a is connected to each of the corresponding front and rear wheels 2 F and 2 R.

The liquid pressure chamber 3 c of the fluid cylinder 3 is connected via a pressure passage 4 with a gas spring 5 , which is divided by a membrane 5 e into a gas chamber 5 f and into a liquid pressure chamber, which in turn is connected to the liquid pressure chamber 3 c of the fluid cylinder 3 is.

With an oil pressure pump 8 , a proportional flow control valve 9 is connected via a liquid pressure pipe passage 10 , which has the function of a flow quantity of the liquid pressure chamber 3 c of each of the fluid cylinders 3 F and 3 R by dispensing oil into or discharging oil adjust from the liquid pressure chamber 3 c.

As shown further in Fig. 1, a pressure gauge Ölabführ designated by the reference numeral 12, with an oil discharge pressure of the oil pressure pump 8 is determined. With the reference numeral 13 designates a fluid pressure sensor to which a fluid pressure of the liquid pressure chamber 3c of each of the fluid cylinders is determined. 3 With the reference sign 14 , a driving height sensor is designated with which the driving height of a vehicle (a cylinder stroke size) of the corresponding wheel 2 F or 2 R is determined. Reference numeral 15 denotes a vertical acceleration sensor which determines a vertical acceleration of the vehicle body (a vertical acceleration of a sprung weight of each of the wheels 2 F and 2 R). Above each of the left and right front wheels 5 F in an approximately horizontal plane of the vehicle body, one of the oil discharge pressure gauges 12 , a liquid pressure sensor 13 , a driving height sensor 14 and a vertical acceleration sensor 15 are arranged. In a central transverse region of the vehicle body between the left and right rear wheels 2 R, an oil discharge pressure meter 12 , the liquid pressure sensor 13 , the driving height sensor 14 and the vertical acceleration sensor 15 are each provided in a corresponding manner. The reference numeral 16 designates a speed sensor is Fahrzeugsge with which a Fahrzeugsge speed of the vehicle is determined. The signals determined by the measuring devices and sensors enter a control device 17 for variable control of the suspension characteristics. This control device is provided with a central processing unit (CPU) etc.

In FIGS. 2A and 2B oil pressure circuits are shown c for controlling a delivery or discharge of oil to and from the fluid pressure chamber 3 are of the fluid cylinder 3. The oil pressure pump 8 is constantly connected to an oil pressure pump 21 for a power steering unit which is to be driven by a drive source 20 . The oil pressure pump 8 is connected via its discharge pipe 8 a to an accumulator 22 . With the discharge pipe 8 a a pipe 23 F for the front derradseite and a pipe 23 R for the rear wheel side are connected on the sides lying downstream in the flow direction; these pipes are arranged parallel to each other. Tung with the provided for the front wheel side F Rohrlei 23 are a conduit 23 FL for the left front wheel side and parallel to it a pipe 23 FR for the right front wheel side connected. The pipe 23 FL for the left front wheel side is connected to the liquid pressure chamber 3 c of the fluid cylinder 3 FL of the corresponding left front wheel 2 FL, while the pipe 23 FR for the right front wheel side with the liquid pressure chamber 3 c of the fluid cylinder 3 FR corresponding to the right front wheel 2 FR is connected. Similarly, the pipe 23 RL for the rear left side with the Flüssigkeitsdruckkam mer 3c of the fluid cylinder 3 FL for the respective rear wheel 2 RL connected, while the pipe 23 RR for the right rear wheel side with the liquid pressure chamber 3c of the fluid cylinder 3 RR corresponding the right rear wheel 2 RR is connected.

Gas springs 5 FL, 5 FR, 5 RL and 5 RR are connected to the fluid cylinders 3 FL, 3 FR, 3 RL and 3 RR. Each of the gas springs 5 FL, 5 FR, 5 RL and 5 RR comprises four gas spring areas, namely a first gas spring area 5 a, a second gas spring area 5 b, a third gas spring area 5 c and a fourth gas spring area 5 d. The four gas spring portions or sections 5 a, 5 b, 5 c and 5 d are parallel to each other through respective branch passages 4 a, 4 b, 4 c and 4 d with respect to a common passage 4 is disposed, the keitsdruckkammer with the liquid 3 c of the fluid cylinder 3 is connected in accordance with the gas spring 5 . The four gas spring sections 5 a, 5 b, 5 c and 5 d are provided at the corresponding branch passages 4 a, 4 b, 4 c and 4 d with openings 25 a, 25 b, 25 c and 25 d; they play a basic function as a suspension device, specifically with the help of their corresponding damping effect and through the buffering action of the gas, which is filled with spring sections 5 a, 5 b, 5 c and 5 d in the gas chamber 5 f. For each of the gas springs 5 FL, 5 FR, 5 RL and 5 RR, a passage between the branch passage 4 a for the first gas spring section 5 a and the branch passage 4 b for the second gas spring section 5 b is provided with a damping force displacement valve 26 , namely for setting a passage area or a passage area of the passage. The damping force shift valve 26 has two positions: a first position is used to open the passage and a second position is used to close the passage. When the vehicle travels around the corner, thus the valve is moved to the second position 26, and thus controls the delivery of the oil to the liquid pressure chambers of the second and third spring portions 5 b and 5 c as well as the removal of the oil therefrom, whereby for the From surrender to the liquid pressure chamber 5 c of the liquid pressure cylinder 3 required oil or the oil required for the removal thereof is limited to a lower value at the time of driving around the corner. In this way, the sensitivity or the stabilization ability with regard to the control with respect to the driving around the corner is improved.

In a corresponding manner, the branch passage 4 d is equipped with a slide valve 27 which has two positions: a first position for opening the branch passage 4 d, and a second position for closing the branch passage 4 d. Moving the shift valve 27 to the first position enables the oil to be discharged to the liquid pressure chamber of the fourth spring portion 5 d or the oil to be discharged therefrom, thereby changing a suspension characteristic to a softer state. When the shift valve 27 is shifted to the second position, the oil discharge to the liquid pressure chamber of the fourth spring portion 5 d or the discharge of the oil therefrom is regulated, thereby changing the suspension characteristic to a harder state. A first suspension characteristic change device 39 is arranged so that the suspension characteristic is changed to a softer state by moving the shift valve 27 to the first position while the suspension characteristic in the second position is changed to a harder state by that the slide valve 27 is pushed ver into the second position.

The discharge pipe 8 a of the oil pressure pump 8 near the battery 22 is connected to a relief check valve 28 , which can assume an open position and a closed position. If the discharge or discharge pressure gauge 12 measures the oil discharge pressure at a value higher than a set upper limit value, then the relief check valve 28 is moved into its open position, whereby the oil of the oil pressure pump 8 returns to a reserve tank 29 and thereby a value for the accumulation of a pressure of the oil of the accumulator 22 is held at a predetermined value. The oil is supplied to each of the fluid cylinders 3 through the oil accumulated in the accumulator 22 .

Since the constructions of the left and right front wheels 2 FL and 2 FR and the left and right rear wheels 2 RL and 2 RR are all the same, only the left front wheel side will be described below, and an explanation of the rest is omitted for the sake of brevity.

According to FIG. 2A, the pipe line 23 FL for the left front of derradseite a proportional flow rate control valve 9 which has three positions: a suspension position, are closed in all connections, a discharge position in which the pipe 23 FL for the left Front wheel side is open, and a discharge position in which the side of the fluid cylinder 3 of the pipe 23 FL for the left front wheel side with a return pipe 32 is in communication. The proportional flow rate control valve 9 is provided with a pressure regulating valve 9 a, which permits the fluid pressure in the liquid pressure chamber 3c of the fluid cylinder 3 at a predetermined value in the feed and Abführstellungen noted.

Furthermore, on the side of the fluid cylinder 3 of the proportional flow control valve 9, a switching valve 33 is provided on or in the pipe 23 FL for the left front wheel side. This valve can be actuated in response to a pilot or control pressure in such a way that it opens or closes the pipeline 23 FL for the left front wheel side. When an electromagnetic valve 34 is opened, a liquid pressure of the pipe 23 FL for the left front wheel side on the oil pressure pump 8 side of the proportional flow control valve 9 is introduced into the valve 33 as a pilot pressure. When the pilot pressure in question reaches a given value or a value above it, the valve 33 is opened and establishes a connection between the proportional flow control valve 9 and the pipe 23 FL for the left front wheel side, thereby enabling the proportional flow control valve 9 to control a flow amount to the fluid cylinder 3 . When the switching valve 33 is closed, the pipeline 23 FL is closed on the left front wheel side in a liquid-tight manner, whereby the prevention of leakage of the oil from the liquid pressure chamber 3c of the fluid cylinder is ensured. 3

As further shown in Fig. 2A, a check valve 35 is connected to the pipe 23 FL for the left front wheel side. This valve serves to return the oil in the return pipe 32, through its opening operation, when the fluid pressure in the Flüssigkeitsdruckkammmer 3c of the fluid cylinder 3 is caused to rise to an abnormally high level.

As shown in FIG. 2A, the valve 36 associated with the ignition key is connected to the discharge pipe 8 a of the oil pressure pump 8 , namely near the accumulator 22 , which is connected to the discharge pipe 8 a; it has the function of relieving a high pressure condition by returning the oil accumulated in the accumulator 22 into the tank 29 when the valve 36 in question is opened after the ignition is switched off. The oil pressure pump 8 is equipped with a relief valve 37 in the pump to lower the oil discharge pressure of the pump 8 by returning the oil to the tank 29 when the liquid pressure is caused to rise to an abnormally high level. With the return pipe 32 , a return accumulator 38 is connected, which acts as a pressure collector when the oil pressure from the fluid cylinder 3 is reduced.

In the following, a description will be given of the control over changes in suspension characteristics by means of the control device 17 , through which the flow amounts of the respective fluid cylinders 3 are controlled. For this purpose, reference is made to FIGS. 3A to 3C. In the drawings, FIG. 3A shows a control system A for controlling a vehicle driving height to a target driving height, namely a cylinder stroke size to a target size. This takes place on the basis of a signal which is determined and generated by means of the ride height sensor arranged on the respective wheel 2 . In Fig. 3B, a control system B is shown, with the help of a vertical vibration of the vehicle based on a signal is reduced, which is determined and generated by means of the three vertical acceleration sensors 15 . FIG. 3C illustrates a control system C which serves to equalize a load on each of the left and right front and rear wheels 2 F and 2 R, on the basis of a signal which is generated by means of the liquid pressure sensors 13 for each of the Wheels is determined and generated.

The control system A is provided with an impact component operation unit 40 , a tilt component operation unit 41, and a roll component component 42 . The recoil component operating unit 40 processes a recoil component of a vibration of the vehicle by summing an output signal X _FL from the ride height sensor 14 for the left front wheel 2 FL and an output signal X _FR from the ride height sensor 14 for the right front wheel 2 FR and by summing an output signal X _RL from the ride height sensor 14 for the right rear wheel 2 RL and the signal X _RR from the ride height sensor 14 for the right rear wheel 2 RR. The tilt component operating unit 41 processes a tilt component of the vibration of the vehicle by subtracting a sum of the output signals X _RL + X _RR from a sum of the output signals X _FL + X _FR . The roll component operating unit 42 processes a roll component of the vibration of the vehicle by adding a difference between the output signals X _FL and X _FR , X _FL - X _FR , on the left and right front wheels 2 FL and 2 FR and a difference between the output signals X _RL and X _RR , X _RL - X _RR on the side of the left and right rear wheels 2 RL and 2 RR.

The recoil component of the vibration of the vehicle operated by the operation unit 40 is then input to a recoil component control unit 43 . In order to control the recoil or recoil component of the vibration, the unit 43 works out a recoil component control quantity for the flow amount control valve 9 of the respective wheel on the basis of a formula of a PD (proportional differential) control as follows:

K _{B 1} + {(T _{B 2} × S) / (1 + T _{B 2} × S)} × K _{B 2}

(where K _{B 1} , K _{B 2} and T _{B 2 are} each a control coefficient, and where S is an operator).

The tilt component of the vibration of the vehicle to which the tilt component operation unit 41 operates is then input to a tilt component control unit 44 which is a tilt component control quantity for the flow amounts Control valve 9 of the respective wheel on the basis of a formula of the PD (proportional differential) control worked out as follows:

K _{P 1} + {(T _{P 2} × S) / (1 + T _{P 2} × S)} × K _{P 2}

(where K _{P 1} , K _{P 2} and T _{P 2} each represent a control coefficient, and where S is an operator).

The roll component of the vibration of the vehicle, to which the roll component operating unit 42 operates, and a target roll angle T _roll are then input to a roll component control unit 45 , which in a corresponding manner developed a rolling component control variable for the flow quantity control valve 9 of the respective wheel on the basis of a formula of the PD (proportional differential) control as follows:

K _{R 1} + {(T _{R 2} × S) / (1 + T _{R 2} × S)} × K _{R 2}

(where K _{R 1} , K _{R 2} and T _{R 2 are} each a control coefficient, and where S is an operator).

To control the ride height to a target ride height, each of the control quantities developed by each of the control units 43 , 44 and 45 for each of the wheels is reversed (the positive (+) and negative (-) directions of the signals which input from each of the ride height sensors 14 are reversed in the opposite directions), and then the recoil, pitch, and roll component control quantities are added to give a control quantity to the proportional control valve 9 for each Wheel to deliver: Q _FL , Q _FR , Q _RL and Q _RR .

The control system B is provided with an impact component operation unit 50 , a tilt component operation unit 51, and a roll component operation unit 52 . The recoil component operating unit 50 works out an impact or recoil component of the vibration of the vehicle by summing up three output signals G _FL , G _FR and G _R from the three vertical acceleration sensors 15 for the left and right front wheels 2 FL, 2 FR and for the rear wheels 2 R. The pitch component operating unit 51 works out a pitch component of the vibration of the vehicle by summing halves of the output signals G _FL and G _FR and then subtracting the output signal G _R from the resulting sum . The rolling component operating unit 52 works out a rolling component of the vibration by subtracting the output signal G _FL on the left front wheel 2 FL side from the output signal G _FR on the right front wheel 2 FR side.

The impact component of the vibration of the vehicle, which is worked out by the recoil component operating unit 50 , is then input to a recoil component control unit 53 , which sets up an impact component or control component for the flow quantity control valve 9 of the respective wheel based on a formula of an IPD (integral-proportional-differential) control as follows:

{T _{B 3} / (1 + T _{B 3} × S)} × K _{B 3} + K _{B 4} + {T _{B 5} × S / (1 + T _{B 5} × S)} × K _{B 5}

(where T _{B 3} , K _{B 3} , K _{B 4} , T _{B 5} and K _{B 5 are} each a control coefficient, and where S is an operator).

The division or distance component of the vibration, which is worked out by the division or distance component operating unit 51 , is then input to a division or distance component control unit 54 , which is a division component control variable for the flow rate control valve 9 of the respective wheel on the basis of an IPD (integral-proportional-differential) control formula as follows:

{T _{P 3} / (1 + T _{P 3} × S)} × K _{P 3} + K _{P 4} + {T _{P 5} × S / (1 + T _{P 5} × S)} × K _{P 5}

(where T _{P 3} , K _{P 3} , K _{P 4} , T _{P 5} and K _{P 5 are} each a control coefficient, and where S is an operator).

The rolling component of the vibration of the vehicle, which the rolling component operating unit 52 develops, is then input into a rolling component control unit 55 , which correspondingly defines a rolling component control variable for the flow quantity control valve 9 of the respective wheel on the basis of an IPD (integral Proportional-differential) tax formula developed as follows:

{T _{R 3} / (1 + T _{R 3} × S)} × K _{R 3} + K _{R 4} + {T _{R 5} × S / (1 + T _{R 5} × S)} × K _{R 5}

(where T _{R 3} , K _{R 3} , K _{R 4} , T _{R 5} and K _{R 5 are} each a control coefficient, and where S is an operator).

In order to control the vertical vibration with the rebound component, the pitch component and the rolling component, each of the control quantities worked out by each of the control units 53 , 54 and 55 per wheel becomes in the same manner as above vice versa, and then the impact component, the division or spacing component and the rolling component control variables are added to thereby obtain a control variable Q _FL , Q _FR , Q _RL and Q _RR for the corresponding fluid cylinders 3 _FL , 3 _FR , 3 _RL and 3 _{RR to} provide. It should be pointed out here that the control variables on the front wheel side, which are worked out by the control units 53 , 54 and 55 , are corrected by a correction coefficient k (k = 1.08), since the loads exerted on the front wheels deviate from those, which are exerted on the rear wheels.

Then, the control system is provided with a C Formänderungs- Verbiegesteuereinheit or 60, which consists on the side of the front wheel of a Belastungsübertragungsverhältnis- Operating unit 60 a and the rear wheel side of a load transfer ratio Betriebsunterein standardized 60 b. The sub-unit 60 a causes a ratio (a load transfer ratio) of a liquid difference (P _FL - P _FR ) between the liquid pressures of the respective left and right front wheels 2 FL and 2 FR to a sum of the liquid pressures of the front wheels by generating signals of the liquid print P _FL and P _FR from the two liquid pressures 13 on the front wheel side. The provided for the rear wheel side load transfer ratio operation subunit 60 b processed on the other hand, a ratio (a Be lastungsübertragungsverhältnis) of a fluid pressure (P _RL - P _RR) difference between the fluid pressures of the respective left and right rear wheels 2 RL and 2 RR to a sum the fluid pressure of the rear wheels by generating signals of the fluid pressure P _RL and P _RR from the two fluid pressure sensors 13 on the rear wheel side. The load transfer ratio on the rear wheel side is then multiplied by a coefficient Wr, and then the product is subtracted from the load transfer ratio on the front wheel side. The difference is then multiplied by a coefficient W _A and then corrected by a correction coefficient (1.08). Then, the control amount for each of the wheels is reversed in the same manner as explained above to achieve smoothness between the left and right wheels, thereby providing the control values Q _FL , Q _FR , Q _RL and Q _RR .

Further, the control value or the control variable Q _FR, which according to FIG be. 3A is obtained, the control value Q _FR, which according to FIG. 3B is obtained, and the control value Q _FR, which according to FIG 3C is obtained., Added to each other, and the resulting sum is finally used as a control value for the flow rate control valve 9 for the right front wheel. In the same way, the control values Q _FL , Q _RR and Q _{RL are} treated and used for the corresponding flow value control valves 9 .

As further shown in FIG. 3C, the second suspension characteristic changer 62 has two modes of operation: NORMAL and SPORT (2). The coefficient Wr in the twist control is changed so that it is variable between the "NORMAL" mode and the "SPORT (2)" mode in accordance with a shift by a manual switch 61 . In other words, this means that the coefficient Wr is set to Wr = 1.5 in the "NORMAL" mode, while it is set to Wr = 1.0 in the "SPORT (2)" mode. When the manual switch 61 is shifted to the "NORMAL" mode, the load transfer ratio on the front wheel side is made larger than that on the rear wheel side by setting the coefficient Wr to 1.5, thereby causing a rolling rigidity ratio on the Front wheel side raised and the suspension characteristics with the tendency of increasing understeer to be changed. When the manual switch 61 is shifted to the "SPORT (2)" program, the load transmission ratio on the front wheel side is made equal to that on the rear wheel side by efficiently setting the coefficient Wr to 1.0. As a result, the suspension characteristics are changed so that the tendency to a usual weak understeer results.

Reference is now made to FIG. 3D; a manual switch 66 is provided to manually shift a suspension characteristic in accordance with a preference of a driver or a driving condition. The manual switch 66 is connected to an operating mode decision unit 67 for the decision of three operating modes: COMFORT (= comfort), SPORT (1) and AUTO. The three modes of operation are manually selected by the manual switch 66 . When the mode decision unit 67 decides that the manual switch 66 has selected the COMFORT mode, a signal Se is generated to change a suspension characteristic to a softer state. In addition, as shown in Fig. 2, the shift valve 27 is turned off to take an open position. When the SPORT (1) operation is decided by the mode decision unit 67 , a signal Sf is generated to change a suspension characteristic to a harder state, whereby the shift valve 27 is adjusted to take a closed position. When the mode decision unit 67 decides the AUTO operation, the shift valve 27 controls an ON / OFF shift in accordance with a vehicle speed to be decided by a vehicle speed decision unit 68 . The vehicle speed decision unit 68 has to compare a vehicle speed V with a preset value Vo in response to a signal of the vehicle speed V, which is determined by means of the vehicle speed sensor 16 . When a driving or driving condition of high speed is determined so that the determined vehicle speed V is equal to or larger than the preset value Vo on the one hand, then the signal Sf is generated to ren the suspension characteristic in a harder Change state, and the shift valve 27 on the front wheel side is only adjusted to take the closed position. When the vehicle speed decision unit 68 decides the existence of a low speed drive state because the determined vehicle speed V is lower than the preset value Vo, the suspension characteristic change signal Se is generated to a softer state to do so Switch off valve 27 so that it assumes an open position.

Fig. 4 illustrates a detail of the operation of the switches 61 and 66. The switch 61 has two actuation keys: an actuation key 61 a, on which the word "NORMAL" is written, and an actuation key 61 b, on which the word "SPORT (2)" is written. The switch 66 has three actuation keys: an actuation key 66 a, on which the word "AUTO" is written, an actuation key 66 b, on which the word "COMFORT" (= comfort), and an actuation key 66 c, on which the Word "SPORT (1)" stands. Each of the actuation buttons 61 a, 61 b, 66 a, 66 b and 66 c can be of such a type of switch that can be actuated when it is pressed. When one of the operation buttons is pressed, the suspension characteristic is selected to correspond to the operation button that has been pressed. The operation buttons 61 and 66 are installed in a position within an instrument panel or the like where the driver can easily operate them.

Reference is now made to FIG. 6, in which a sketch of the construction of the vehicle is shown, which was the subject of the four-wheel steering. Reference numerals 81 L and 81 R denote left and right front wheels, while reference numerals 82 L and 82 R denote left and right rear wheels. The left front wheel 81 L is connected to the right front wheel 81 R via a front wheel steering mechanism 83 , while the left rear wheel 82 L is connected to the right rear wheel 82 R via a rear wheel steering mechanism 84 .

The front wheel steering mechanism 83 includes a pair of link arms, namely a left link arm 84 L and a right link arm 84 R, a pair of steering rods, namely a left tie rod 85 L and a right track rod 85 R, and a front wheel Handlebar 86 , which connects the tie rods 85 L and 85 R. With the reference numeral 87 , a steering wheel is designated, which is connected to a shaft or a shaft 88 . At a lower end portion of the shaft 88 in question is a pinion 89 is brought, which meshes with a rack 90 which is attached to the front wheel handlebar 86 . The front wheels 81 L and 81 R are steered by shifting the front wheel handlebar 86 in accordance with the operation of the steering wheel 87 .

According to the front wheel steering mechanism 83, the rear wheel steering mechanism 84 includes a pair of left and right th link arms 93 L, 93 R and a pair of left and right th link rods 94 L, 94 R and a rear wheel steering rod 95 . With the rear wheel handlebar 95 a Ver slowdown or braking mechanism 96 is connected, which in turn is connected to an output shaft 97 a of a servo motor 97 . The rear wheels 82 L and 82 R are steered by the fact that a transmission to the rear wheel handlebar 95 is carried out by the deceleration or braking mechanism 96 , as a result of the rotation of the servo motor 97th

In the rear wheel steering mechanism 84 , the Abtriebswel le 97 a of the servo motor 97 is provided with an electromagnetic brake 100 , which is designed so that it locks the output shaft 97 a of the motor and the rear wheel handlebar 95 during their braking action, whereby a steering condition or the steering condition of the rear wheels 82 L and 82 R is maintained. Between the output shaft 97 a of the servo motor 97 and the deceleration mechanism 96 , an electromagnetic clutch 101 is arranged. The rear wheel handlebar 95 is provided with a position feedback mechanism 102 which returns the rear wheel handlebar 95 to a neutral position. If the rear wheels are steered in an abnormal way, the opened electromagnetic clutch 101 to the rear-wheel steering bar to be separated 95 from the servo motor 97, whereby the rear wheel turning rod is returned 95 to its neutral position by means of the position feedback mechanism 102 . As a result, the rear wheels 82 L and 82 R are set to their neutral position, in which their steering angle is zero.

With the reference sign 110 a control device is designated, which serves to control a steering angle of the rear wheels. The control device 110 basically controls the servo motor 97 and the electromagnetic brake 100 . The control device 110 receives signals from various sensors 115 to 126 and from the switches 61 and 66 . The sensor 115 is a steering angle sensor, and the sensor 116 is a front wheel steering angle sensor for determining a steering angle of the front wheel by a value by or according to which the front wheel steering rod 86 is moved. Reference numerals 117 and 118 denote two vehicle speed sensors, and reference numeral 119 denotes a neutral clutch switch, which is used to determine the N (neutral) position of a manual transmission and a time at which a clutch pedal ge is kicking. The reference numeral 120 designates a lock switch which determines the N position or P (park) position of an automatic transmission. Reference numeral 121 denotes a brake switch with which a point in time is determined at which a brake pedal is depressed. Reference numeral 122 denotes a motor switch which determines the point in time at which the motor is running. Reference numeral 123 designates a rotation angle sensor which indicates a rotation angle of the servo motor 97 . Reference numeral 124 denotes a rear wheel steering angle sensor which determines a steering angle of the rear wheels from a value by which the rear wheel steering rod 95 has been displaced or shifted.

The control device 110 , which serves to control the rear wheel steering angle, previously stores a rear wheel steering characteristic, as illustrated in FIG. 5. The rear wheel steering characteristic, which is illustrated in Fig. 5, is given by characteristics, according to which a rear wheel steering ratio, namely a ratio of a rear wheel steering angle R _R to a front wheel steering angle R _F (wherein the front wheel steering angle R _F is proportional to a steering angle H) with a vehicle speed and changes from one and the same phase side to an opposite phase side in accordance with a transition from a low vehicle speed to a high vehicle speed. As shown in Fig. 5, the curve no. 1 represented by the solid line is set so that the steering characteristic on the same phase side of the curve no. 2, which is indicated by the dashed line, deviates at the same vehicle speed.

Returning to FIG. 6, it should be noted that a steering control device 128 is arranged to control the rear wheel steering mechanism 84 in accordance with the characteristic No. 1 or No. 2 shown in FIG. 5 by means of the control device 110 for controlling a steering angle the rear wheels controls.

Each of the control devices 67 and 110 for changing the suspension characteristic and for controlling the rear wheel steering ratio has the function of receiving and outputting signals selected by each of the manual switches 61 and 66 . The controller 110 has the function of selecting the steering characteristics of the rear wheels in accordance with the mode of operation obtained by shifting the characteristic No. 1 or No. 2 shown in FIG. 5 in accordance with the table shown below. As described above, the controller 110 includes a steering characteristic storage means in which the two steering characteristics as shown in Fig. 5 are stored in a read only memory ROM. A steering characteristic selection device is also provided, which selects one of the two steering characteristics in each case in accordance with the table below.

table

A steering characteristic correction means 130 is arranged so that the rear wheel steering characteristic on the characteristic No. 1 or No. 2 as shown in FIG. 5 is corrected in synchronization with the suspension characteristic, which is by means of the first or second suspension characteristic changing means 39 or 62 to be changed in accordance with the control shown in the table above. Particularly when the suspension characteristic is changed by the second suspension characteristic changer 62 to show the tendency according to which understeer is reduced by setting the coefficient Wr for twist control to 1.0 when the manual switch 61 is manually shifted to SPORT (2) operation, as illustrated in point 6 of the table above, then the steering characteristic correction device 130 corrects the rear wheel steering characteristic on the reverse phase side with respect to the front wheels by the characteristic curve Nr. 1 of FIG. 5 in synchronization with the amendments tion of the suspension characteristic is set, with a decreasing understeer tendency.

When the manual switch 66 is shifted to the AUTO mode as illustrated in position 4 of the above table, and the vehicle speed V is set to such a high driving speed that it is equal to or larger than the set one Value Vo is, then the shift valves 27 are switched on only for the front wheels, as shown in Fig. 2, to assume the closed position. This enables the first suspension characteristic changing means 62 to change the suspension characteristic to a harder state on the front wheel side and a softer state on the rear wheel side with a tendency to understeer increasing. In this case, the rear wheel steering characteristic is set to the characteristic No. 1 as shown in FIG. 5, and it is corrected to the reverse phase side with respect to the front wheels in synchronization with the change in the suspension characteristic.

If the manual switch 66 is pushed ver into the COMFORT position, as indicated in position 1 of the table above, the slide valve 27 is switched off and moved into the open position. This enables the oil to be delivered to or discharged from the fourth spring 5 d of each of the gas springs 5 FL, 5 FR, 5 RL and 5 RR and to change the suspension characteristic by the amount concerned into a softer state. In synchronization with the change in the suspension characteristic, the rear-wheel steering characteristic is selected so that it is fixed to the steady-state characteristic curve No. 2 according to FIG. 5. As a result, a favorable or advantageous steerability or controllability of the vehicle can be achieved by a soft driving comfort with a good mileage or driving performance.

When the manual switch 66 is shifted to the SPORT (1) position, as illustrated in position 2 of the table above, the shift valve 27 is shifted to the closed position, thereby causing oil discharge or discharge to or from the fourth springs 5 d is regulated. Accordingly, the suspension characteristic changes by a degree to a harder state. The steering characteristic on the front wheel side is corrected to the reverse phase side opposite to the rear wheel by the fact that the rear wheel steering characteristic from the stationary characteristic No. 2 to the characteristic No. 1, as shown in Fig. 5, in synchronization with the change is selected in the suspension characteristics. As a result, a favorable or advantageous sport union driving style or driveability or steerability can be achieved in that a relatively hard driving comfort is combined with a sharp or violent movement of the vehicle.

When the manual switch 61 is shifted to the SPORT (2) position as shown in the position 6 of the above table, the connection control coefficient Wr is set to 1.0 and the load transmission ratio on the front wheel side is identical to that made on the rear wheel side. This changes the suspension characteristics so that the tendency of the understeer is reduced. In synchronization of this change, the characteristic No. 1, as shown in Fig. 5, is selected as the rear wheel steering characteristic, and the rear wheel steering characteristic is corrected so that it lies on the opposite phase side with respect to the front wheels. Accordingly, the tendency to reduce understeer is further promoted, whereby an advantageous or favorable sport driving style or steerability and stability are achieved.

During a period of high-speed driving, that is, when the vehicle speed V is equal to or higher than the set value Vo, in the case where the manual switch 66 is shifted to the AUTO mode as shown in FIG the position 4 of the above table is specified, only the shift valves 27 are turned on on the front wheel side and moved to the closed position, whereby the suspension characteristic on the front wheel side is changed to a harder condition and on the rear wheel side to a softer condition. As a result, the driver can enjoy a feeling of driving stability and a favorable or advantageous driving comfort of the vehicle. At that time, the load transmission ratio on the front wheel side becomes larger than that on the rear wheel side, accompanied by the suspension characteristic on the front wheel side in a harder state. This changes the suspension characteristic so that the tendency to understeer increases. However, the characteristic curve 1, as shown in FIG. 5, is selected as the rear wheel steering characteristic; it is corrected so that it is on the reverse phase side ent opposite to the front wheels, in synchronization with the change in the suspension characteristic. As a result, the tendency of increasing understeer is regulated and eliminated, and the effect of the suspension characteristics on the driveability or steerability of the vehicle is reduced. As a result, the performance when driving around the corner can be increased with an advantageous stability in connection with driving comfort of the vehicle, even during a driving period at high speed, whereby the drivability or the steering ability is improved.

Although the above description has been directed to the suspension device with the gas springs 5 , it should be understood that the present invention can be applied to a suspension device in which no gas spring is provided and in which only the fluid cylinder 3 is mounted in this way is that the suspension characteristic is changed.

Claims (23)

1. Control device for a vehicle, with a device ( 39 , 62 ) for changing a suspension characteristic,
a rear wheel steering mechanism ( 84 ) for steering the rear wheels ( 82 L, 82 R) and a control device ( 110 ) for controlling the rear wheel steering mechanism ( 84 ) based on a predetermined steering characteristic,
characterized in that a correction device ( 130 ) changes the steering characteristic simultaneously with a change in the suspension characteristic in the sense of supporting the changed suspension characteristic. 2. Device according to claim 1, characterized in that the steering characteristic correction device ( 130 ) corrects the steering characteristic in the direction of the reverse phase side synchronously with the change in the suspension characteristic by the suspension characteristic changing device ( 39, 62 ) in the direction of increasing vehicle understeer. 3. Apparatus according to claim 1, characterized in that the correction device ( 130 ) corrects the steering characteristic in the same phase side synchronously with the change in the suspension characteristic by the device ( 39, 62 ) for changing the suspension characteristic in the direction of decreasing vehicle understeer. 4. Device according to one of the preceding claims, characterized in that the steering characteristic correction device ( 130 ) has a storage device for storing the steering characteristic according to the suspension characteristic and a selection device ( 110 ) which selects the steering characteristic from a plurality of steering characteristics stored in the storage device, wherein each steering characteristic is associated with a suspension characteristic that changes the suspension characteristic changing means ( 39, 62 ). 5. Device according to one of the preceding claims, characterized in that the suspension characteristic changing device ( 39, 62 ) sets the suspension characteristic between a first state and a second state, the damping of a suspension being softened only in the first wheels in the first state, whereas in the second state the damping is only set hard on the front wheels, and that the steering characteristic correction device ( 130 ) corrects the steering characteristic in the direction of the opposite phase side when the suspension characteristic is set in the first state, in comparison with the change in the latter second state. 6. The device according to claim 5, characterized in that the suspension characteristic changing means ( 39, 62 ) changes the suspension characteristic in the first state when a vehicle speed is low as a parameter, while the change in the second state occurs when the vehicle speed is high is. 7. The device according to claim 1 to 4, characterized in that
that the suspension characteristic changing means ( 39, 62 ) sets the suspension characteristic between a state and a second state, wherein a roll stability ratio of the front wheel side to the rear wheel side is large in the first state and small in the second state,
and that the steering characteristic correcting means ( 130 ) changes the steering characteristic toward the reverse phase side when the suspension characteristic is changed to the first state compared to the change thereof to the second state. 8. Device according to one of the preceding claims, characterized in that the suspension characteristic changing device ( 39, 62 ) sets the suspension characteristic by changing the damping of a suspension. 9. Device according to one of the preceding claims, characterized in that the suspension characteristic changing device ( 39, 62 ) sets the suspension characteristic by changing a roll stability ratio of the front wheel side to the rear wheel side. 10. Device according to one of the preceding claims, characterized in that a suspension comprises a cylinder unit ( 3 ) and a gas spring connected to the cylinder unit ( 85 ) and that the cylinder unit is arranged between the sprung mass and the unsprung mass of each wheel, that a driving height of the vehicle is set according to the delivery of an operating fluid to the cylinder unit ( 3 ) or the discharge of the fluid from the cylinder unit. 11. The device according to claim 10, characterized in that a variable opening between the cylinder unit ( 3 ) and the gas spring ( 85 ) is inserted and that the suspension characteristic changing device ( 39, 62 ) changes a damping in that the variable opening is controlled . 12. The apparatus according to claim 10 or 11, characterized in that a suspension control device ( 17 ) is provided which controls the delivery of the actuating fluid to the cylinder unit ( 3 ) or the discharge of the actuating fluid from the cylinder unit according to a certain state, and that the suspension characteristic changing means ( 39, 62 ) changes the determined state. 13. The apparatus according to claim 12, characterized in that a pressure detection device ( 13 ) is provided, which detects the pressure in the respective cylinder unit ( 3 ), and that the suspension control device ( 17 ) has a twisting or deformation force between one controls front part of a vehicle body and a rear part of the vehicle body in dependence on an output signal of the respective pressure detection device. 14. Device according to one of the preceding claims, characterized in that the suspension characteristic changing device ( 39, 62 ) corrects the torsional force of either the front area or the rear area of the vehicle body. 15. The device according to one of claims 1 to 12, characterized in that
that a pressure detection device ( 13 ) is provided which detects the pressure in the respective cylinder unit,
that the suspension control device ( 17 ) comprises a first ratio detection device and a second ratio determination device,
that the first ratio device is used to detect a first ratio of a sum to a difference, the sum being obtained by adding two output values of two pressure devices for cylinder units which are arranged on the front wheels, and the difference being obtained thereby an output value for one of the two pressure devices for the front wheels is subtracted from the other output value for the other of the two pressure devices,
that the second ratio device serves to determine a second ratio of a sum to a difference, the sum is obtained by adding two output values of two pressure devices for the cylinder units used on the rear wheels,
that the difference is obtained by subtracting an output value for one of the two pressure detection devices for the rear wheels from the other output value of the other pressure device of the two pressure devices,
and that the suspension characteristic changing means ( 39, 62 ) corrects a ratio of the first and second ratios. 16. Device according to one of the preceding claims, characterized, that the steering characteristic is set with a vehicle speed as a parameter is. 17. The apparatus of claim 16, characterized, that the steering characteristic is set so that the rear wheels continue to the same Phase side are steered if the vehicle speed is greater than that In case it is lower.   18. The apparatus of claim 16 or 17, characterized in that the rear wheels ( 82 L, 82 R) are steered in a direction opposite to the front wheels when the vehicle speed is lower than a predetermined vehicle speed, or in that the rear wheels in the same direction as the front wheels are steered when the vehicle speed is greater than the predetermined speed. 19. Device according to one of the preceding claims, characterized by selection means ( 61 , 66 ) for the manual selection of one of several characteristic combinations,
the suspension characteristic being set according to the combination selected by the selection means ( 61 , 66 ), and
wherein the steering characteristic is set according to the selected combination by the selection means ( 62 , 66 ). 20. The apparatus according to claim 19, characterized in that the selection means ( 62 , 66 ) further enable automatic selection, so that a predetermined combination of characteristics is automatically selected depending on a predetermined condition. 21. The apparatus according to claim 20, characterized, that the condition is a vehicle speed as a parameter used. 22. The device according to one of claims 19 to 21, characterized in that
that a first suspension characteristic (characteristic curve 1) for the hard position of the suspension of the front and rear wheels and a second suspension characteristic (characteristic curve 2) for the soft position of the suspension of the front and rear wheels are provided,
that a first and a second steering characteristic are provided on the same phase side, and
that the characteristic combination comprises a combination of the first suspension characteristic with the first steering characteristic and a combination of the second suspension characteristic with the second steering characteristic. 23. The device according to one of claims 19 to 21, characterized in that
that a first suspension characteristic (characteristic curve 1) for the hard position of the suspension of the front wheels ( 81 L, 81 R) and a second suspension characteristic for soft adjustment of the suspension of the front wheels ( 81 L, 81 R) are provided, a first and a second steering characteristic on the same phase side are provided, and
that the characteristic combinations comprise a combination of the first suspension characteristic with the first steering characteristic and a combination of the second suspension characteristic with the second steering characteristic.